1. Field of the Invention
The present invention relates to a semiconductor device including an oxide semiconductor and a manufacturing method thereof.
In this specification, the semiconductor device refers to all the devices that can function by utilizing semiconductor characteristics. A transistor described in this specification is a semiconductor device, and an electrooptic device, a semiconductor circuit, and an electronic device which include the transistor are all semiconductor devices.
2. Description of the Related Art
Transistors used for most flat panel displays typified by a liquid crystal display device and a light-emitting display device are formed using silicon semiconductors such as amorphous silicon, single crystal silicon, and polycrystalline silicon provided over glass substrates. Further, transistors formed using such silicon semiconductors are used in integrated circuits (ICs) and the like.
Attention has been directed to a technique in which, instead of the above silicon semiconductors, metal oxides exhibiting semiconductor characteristics are used for transistors. Note that in this specification, a metal oxide exhibiting semiconductor characteristics is referred to as an oxide semiconductor.
For example, a technique in which a transistor is manufactured by using zinc oxide or In—Ga—Zn-based metal oxide as an oxide semiconductor, and the transistor is used as a switching element or the like of a pixel of a display device is disclosed (see Patent Documents 1 and 2).
[Reference]
[Patent Document]
    [Patent Document 1] Japanese Published Patent Application No. 2007-123861    [Patent Document 2] Japanese Published Patent Application No. 2007-096055